1. Field of the Invention
The present invention relates to a hydraulic vibration-isolator which is applicable, for instance, to hydraulic suspension-bushings used as a vibration-insulating member for suspension mechanisms installed onto vehicles.
2. Description of the Related Art
In a suspension mechanism installed onto a vehicle, there has been provided a hydraulic vibration-isolator for decreasing vibrations resulting from a road surface or a vehicle tire. The hydraulic vibration-isolator is installed, for instance, at an L letter-shaped lower arm of a FR suspension mechanism in such a manner that an axial direction of the hydraulic vibration-isolator corresponds to a length direction of the vehicle. In this case, as for the hydraulic vibration-isolator, a main axis fitting thereof is fixed to the lower arm, an outer cylinder-shaped fitting is fixed to a supporting member of the vehicle body, partition walls thereof are disposed in a vertical direction of the vehicle, and a pair of divided fluid chambers thereof is disposed in a width direction of the vehicle. When vibrations are inputted between the main axis fitting and the outer cylinder-shaped fitting, the vibrations can effectively be damped on the basis of an elastic function of a rubber elastic member and on the basis of a fluid-column-resonating action caused by a fluid which flows in the fluid chamber owing to the elastic function of the rubber elastic member.
In such a way, the hydraulic vibration-isolator, utilizing fluid-column-resonating action caused by the fluid flowing in the fluid chamber, is constituted to decrease load noises, vertical vibrations transmitted from the road surface and the vehicle tire.
Recently, decrease of load noises is further requested. So, as ways for achieving this request, it is thought that a rubber material having a low spring property and a static spring constant in a vertical direction is desired.
Such materials, however, decrease a frequency region of fluid-column-resonating action utilizing the inner stopper to lower regions. When a frequency region of the fluid-column-resonating action decreases to a practical frequency region, i.e. a frequency region of less than 500 Hz, it is possible to use a fluid-column-resonating action for isolating vibrations. However, the fluid-column-resonating action surely exerts anti-resonance which effects a bad influence in decreasing the load noises.